1. Technical Field
The present invention relates to an system, method and program for controlling execution sequencing of multiple jobs to improve overall job execution efficiently and, more particularly, to an system, method and program for controlling the execution timing of jobs in such a manner that while execution of one job occurs at irregular and singularly unforeseeable time intervals, another job can be executed while limiting execution overlap with the former.
2. Description of the Related Art
An example of a multi-job processing scenario occurs in a tape drive that is externally connected to a computer, wherein a function diagnosis program is executed. As part of the function diagnosis program, it may be useful to check in advance the possibility of failure due to degradation with time in a portion of a memory. Conventionally, such a function diagnosis program is executed at regular time intervals.
Published Unexamined Patent Application No. 5-242103 discloses a job scheduling system in which a plurality of jobs to be executed successively can be executed with efficiency in spite of occurrence of machine failure with certain probability. In this scheduling system, the maximum, average, and minimum time periods allocated to jobs in a machine are computed. The time allocated for each job is divided into three (first to third) time segments, and the first segment for one job is suitably positioned in time relative to the third segment for the preceding job. That is, the subsequent job earliest and latest start times are suitably set relative to the preceding job earliest and latest end times.
Ordinarily, a tape drive is a single-tasking device and executes processing for reading data from or writing data to a tape as its essential job. If such a tape drive receives an instruction to read or write data while executing a function diagnosis program, it must wait before executing the regular job. Even in the case of a device capable of multitasking, execution of processing based on a function diagnosis program or the like during execution of regular processing often leads to a reduction in the speed of the regular processing or occurrence of a failure.
The scheduling system disclosed in Published Unexamined Patent Application No. 5-242103 is effective in allocating to a machine a plurality of jobs with substantially fixed execution start times and execution order. However, it is incapable of scheduling a plurality of jobs in a machine in which requests for execution of a regular job occur unforeseeably. The present invention addresses the foregoing shortcomings in prior art job scheduling techniques.